Denis

return [
'components' => [
    'db1' => [
        'class' => 'yii\db\Connection',
        'dsn' => 'mysql:host=localhost;dbname=db1name', 
        'username' => 'db1username',
        'password' => 'db1password',
    ],
    'db2' => [
        'class' => 'yii\db\Connection',
        'dsn' => 'mysql:host=localhost;dbname=db2name', 
        'username' => 'db2username',
        'password' => 'db2password',
    ],
],
];

Yii::$app->db1->createCommand((new \yii\db\Query)->select('*')->from('tbl_name'))->queryAll();
Yii::$app->db2->createCommand((new \yii\db\Query)->select('*')->from('tbl_name'))->queryAll();

public static function getDb() {
    return Yii::$app->db2;
    // return Yii::$app->db1;
}

SELECT dta.id, dta.doc_name, dta.doc_title, dta.link, dta.status, GROUP_CONCAT(DISTINCT dty.doc_id ORDER BY dty.doc_id ASC SEPARATOR ', ') AS type_id
FROM doc_table dta
INNER JOIN docs_types dty ON dta.id=dty.doc_id
GROUP BY dta.id;

SELECT dta.id, dta.doc_name, dta.doc_title, dta.link, dta.status, GROUP_CONCAT(DISTINCT t.type_name ORDER BY t.id ASC SEPARATOR ', ') AS type_name
FROM doc_table dta
INNER JOIN docs_types dty ON dta.id=dty.doc_id
INNER JOIN types t ON t.id=dty.type_id
GROUP BY dta.id;

$('body').on('change', '#mySelect', function() {
    $('#myButton').attr('data-id', $(this).val());
});
// Если не устанавливаются значения по-умолчанию можно поступить и так.
$('#mySelect').change();